GB786399A - Method and apparatus for continuously drawing a glass sheet - Google Patents

Abstract

786,399. Glass drawing. COMPAGNIES REUNIES DES GLACES ET VERRES SPECIAUX DU NORD DE LA FRANCE. Jan. 19, 1956 [Jan. 24, 1955], No. 1823/56. Class 56. Relates to the drawing of a continuous ribbon of glass from a tank in a substantially horizontal direction. The bottom of the drawing tank 2 slopes upwardly to a fairly long spout 6 wherein the depth of the glass is but little greater than the thickness of the ribbon to be formed. The bottom of the tank and the spout are heated by conduction, by electric heaters 10, 14 and the surface of the glass is cooled, by convection by water-cooled air-blowing and suction tubes 15, 17, 19, 20. The spout, at least, is made from a material of low overall emissivity e.g., pure, or substantially pure, alumina, magnesia or silica, ,and the spout may be a separate member removable from the pot 2. Alternatively the spout may be made of ordinary silico-aluminous material the bottom and sides of which are covered by an electrically heated platinum sheet. The vault 22 of the spout may be made of material of high emissivity, e.g., magnesia or chrome-magnesia containing more than 5 per cent iron oxides which ensures that heat radiated from the glass is reflected back. Alternatively the lower face of the vault may be lined with a platinum sheet. These features, taken together, ensure that a maximum temperature gradient is established between the upper and lower surfaces of the glass in the spout whereby the stream of glass comprises a film of high mobility at its lower surface and a skin of high viscosity at its upper surface. The lower surface of the sheet is rapidly hardened by blower and suction tubes 27, 28 immediately after leaving the spout. The spout may be slightly concave along its longitudinal axis and the lateral walls may have longitudinal rounded grooves along their inner edges. Specification 782,149 is referred to.